Low Temperature Activation of Tellurium and Resource-Efficient Synthesis of AuTe₂ and Ag₂ Te in Ionic Liquids

The low temperature syntheses of AuTe₂ and Ag₂ Te starting from the elements were investigated in the ionic liquids (ILs) [BMIm]X and [P₆₆₆₁₄ ]Z ([BMIm]⁺ =1-butyl-3-methylimidazolium; X = Cl, [HSO₄ ]^- , [P₆₆₆₁₄ ]⁺  = trihexyltetradecylphosphonium; Z = Cl^- , Br^- , dicyanamide [DCA]^- , bis(trifluoromethylsulfonyl)imide [NTf₂ ]^- , decanoate [dec]^- , acetate [OAc]^- , bis(2,4,4-trimethylpentyl)phosphinate [BTMP]^- ). Powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy revealed that [P₆₆₆₁₄ ]Cl is the most promising candidate for the single phase synthesis of AuTe₂ at 200 °C. Ag₂ Te was obtained using the same ILs by reducing the temperature in the flask to 60 °C. Even at room temperature, quantitative yield was achieved by using either 2 mol % of [P₆₆₆₁₄ ]Cl in dichloromethane or a planetary ball mill. Diffusion experiments, ³¹ P and ¹²⁵ Te-NMR, and mass spectroscopy revealed one of the reaction mechanisms at 60 °C. Catalytic amounts of alkylphosphanes in commercial [P₆₆₆₁₄ ]Cl activate tellurium and form soluble phosphane tellurides, which react on the metal surface to solid telluride and the initial phosphane. In addition, a convenient method for the purification of [P₆₆₆₁₄ ]Cl was developed.